Applicant claims priority under 35 U.S.C. .sctn.119 based upon PCT Patent Application PC/DE95/008743 filed Jul. 6, 1995, and German Patent Application P44 23 921.1 filed Jul. 7, 1994.
1. Field of the Invention
The present invention relates in general to flexible piping, and, more specifically to a flexible pipe used to connect rigid media conducting underground supply pipes comprising a metal corrugated bellows (or pipe) with connecting elements provided on both ends and a flexible wrap (or jacketing) extending along the entire length of the corrugated bellows and at least a part of one or both of the connecting elements.
2. Background Art
In mining areas, the surface of the earth often includes sink holes, fissures and compressions of the ground. Consequently, pipes that are layed in the ground are, over time, often displaced, pulled and buckled. Damage to the supply through these pipes often results if no elements are provided that can compensate for these movements. A particular potential for danger is inherent in gas pipe lines, wherein damage to the pipes may result in the leaking of gas, and, in turn, ignition of such a gas-air mixture.
Generally, supply pipes that are under low pressure and/or those that have nominal widths up to about DN 150 are often constructed of plastic material. Older supply pipes that have existed for years as well as newer pipes greater than DN 150 and/or those capable of withstanding higher pressures are constructed of steel or other metals. The steel/metal pipes are usually provided with plastic corrosion protection.
Gland extenders are disclosed in German patents DE OS 39 39 956, DE 28 53 726 and DE OS 37 02 693 as comprising an inner and an outer pipe wherein the pipes can move axially relative to each other. An elastomeric gasket or gland packing prevents the outflow of the gas from the pipe. A fundamental disadvantage of such an extender having the gaskets arises when the extender has undergone one or more displacements. Under such conditions, the extender is capable of developing leaks, permitting gas to flow out into the atmosphere, resulting in a dangerous condition. Further, dangerous conditions may result from the outflow of gas which follows along the pipe and, under certain circumstances, enters into buildings which are fed by the pipes.
Another disadvantage of the extender with gaskets is that the absorption of lateral or angular movements is generally non existent, or minimal at best. Thus, if lateral forces are imposed, leaks may develop in the pipes.
Generally, the above described extender comprises two flanges with the gasket therebetween, wherein the flanges are pressed against each other in order to provide the necessary compression for the gasket. If the extender must be insulated for purposes of corrosion protection, any parts that deviate from a cylindrical shape are difficult to insulate. To provide the proper insulation, it is also a disadvantage that the entire extension of the element is positioned only at a point at which the inner pipe leads into the outer pipe. A covering has to be produced that absorbs the entire displacement/movement at the point of entry. In sum, a cost effective and overall adequate solution is virtually impossible with this type of construction.
Corrugated pipes, corrugated hoses and compensators--bellows--for the purpose of equilibrating movements in steel pipes are also known. They are generally comprised of a stainless steel which is substantially flexible. As such, they require no addition of gaskets. These corrosion protected corrugated pipes are preferably used with underground pipes up to DIN 100.
German Patent DE 25 58 478 specifies a corrugated hose with a pipe stub connected at both ends which bears a covering composed of a shrink wrap hose for corrosion protection. The metallic corrugated hose on the inside is well suited for longitudinal, traverse and angular movements. The shrink wrap hoses are constructed by pre-extending them to larger diameters, then polymerizing them by radiation. These hoses are then shrunk back to the original narrower diameter (previous to the extension) upon application of heat. A covering that is comprised of shrink wrap hose is, however, only extendible to a limited extent.
The axial extendibility of PE shrink hoses which are suitable for corrugation for laying underground pipes do not, when overlayed, achieve the extendibility of the underlying stainless steel corrugated hoses. German Patent DE 97 46 08 specifies a wrapped metal hose with a PVC jacket, however the problems relating to axial extension are unfortunately the same. German Patent DE OS 37 02 676 specifies a corrugated hose having a braiding and a shrink wrap hose/coating, however, due to the braiding, axial extension is not possible. Moreover, while it is also known to apply viscous bitumen to metal corrugated hoses to form a coating, the ability for the hose to extend is limited after the bitumen mass has cooled.
Until now, the binding of a stainless steel bellows was wrapped with an overlap from winding to winding. G94 04 814.2 specifies the possibility of achieving axial extension by means of an elongated covering which comprises a corrosion protective wrapping that is separated from the corrugated surface. However, when axial extendibility is the most important characteristic for compensators, and previous jacketings have not achieved the axial extendibility of metal bellows, a jacketing that features greater extendibility is necessary.